Control of plant diseases and pests is an inevitable work in efficiently performing the agricultural production, and in order to achieve this purpose, synthetic pesticides have been used, resulting in making a remarkable achievement. However, in recent years, there have been taken up the appearance of chemical-resistant insect pests and the issue of environmental disruption to be caused due to administration of large dose of synthetic pesticides, and how to reduce the environmental load, thereby performing the agricultural production efficiently and continuously has become an important problem in the agricultural field.
As one of solution strategies thereof, microbial pesticides utilizing functions of microorganisms are proposed. By a single use or combined use thereof with a synthetic pesticide, an effect for reducing the environmental load and an effect for suppressing the frequency of appearance of resistant diseases and pests, which is a serious problem in the synthetic pesticides, are perceived.
At present, as microorganisms which are expected to be utilized as microbial pesticides, non-pathogenic Fusarium capable of activating the resistance which a plant originally possesses to control the disease injury; Trichoderma exhibiting antibiotic activity against pathogenic microbes; filamentous fungi that are a pathogenic fungus against insect pests; bacteria which infect weeds; and the like are proposed.
In this way, a variety of microorganisms having possibility as pesticides have been proposed. However, in developing microbial pesticides, namely microbial agent for controlling a plant disease and/or a pest, how to make a microorganism that is an active component into a formulation stably in a viable cell state is a key, and the extinction of microorganisms during the preservation period, or the like is an obstacle. In consequence, the development of a method for preserving a microorganism stably in a living state for a long period of time is an important problem.
Now, as for general preservation methods of microorganisms, there are known a freeze-drying method, a method of storing cultures under paraffin oil, a slant medium method, and the like. But, though all of these methods are effective in the case of handling a small-scale amount of microorganisms, they are not suitable as a preservation method of microbial pesticides in which handling of a large amount of microorganisms and a large number of viable cells are required.
On the other hand, as for microbial pesticides or formulations of microbial materials, there have hitherto been known a formulation obtained by adsorbing a microorganism belonging to the genus non-pathogenic Fusarium onto a zeolite-based substrate and spontaneously drying it (Patent Document 1); an agent for controlling a plant disease utilizing a sporal fraction of a bacterium belonging to the genus Bacillus (Patent Document 2); a composition obtained by mixing an adsorbent having ammonia-adsorbing ability with microorganisms having a controlling effect against the plant disease injury (Patent Documents 3 and 4); a composition composed of endospores of Bacillus subtilis and a chemical fungicide component (Patent Document 5); and the like.
However, in the above-described formulation in which viable cells of Fusarium are adsorbed onto a zeolite-based substrate, there is a tendency that when preserved at room temperature, the number of viable cells rapidly decreases; and in the case of agent for controlling a plant disease utilizing a sporal fraction of cells belonging to the genus Bacillus, how its preservability changes is not known at all. Moreover, in the case of microorganism materials, since the substrate used as a culture medium is incorporated as it is, there is involved such a problem that nutrient components exist and promote the growth of pathogenic microbes during the preservation. On the other hand, the above-described composition having an adsorbent having ammonia-adsorbing ability mixed therewith involved such problems that in pesticide formulations including the addition of water during the formulation step, they cannot be applied because of deactivation of the adsorbing ability of the adsorbent to be caused due to the addition of water; and that sufficient preservation stability is not always obtained in the long-term preservation over several years. In addition, the mixed composition of endospores of Bacillus subtilis and a chemical fungicide involved such a problem that the viable spores decrease due to the chemical fungicide component to have been mixed.